Image forming apparatuses in which a toner image formed on a photosensitive member is transferred to a recording medium through an intermediate transfer member and heat fixed to the recording medium by a fixing device have been widely used.
In such an image forming apparatus, untransferred toner that has not been transferred by a transfer unit, which transfers the toner image to the recording medium, is collected by a cleaning blade. The cleaning blade disposed between the transfer unit and an image forming unit is in contact with the intermediate transfer member. The cleaning blade also collects a toner image for control (patch image), which is not to be transferred to the recording medium. Furthermore, the cleaning blade collects the toner when jamming of the recording medium occurs during image formation.
In the image forming apparatus in which the cleaning blade disposed between the transfer unit and the image forming unit is in contact with the intermediate transfer member as described above, paper dust and toner clumps are caught by a blade edge as the number of times of image formation increases. This may cause the toner to passing through the cleaning blade.
In order to address this, according to PTL 1, an intermediate transfer belt is stopped and rotated in a reverse direction by a specified distance after completion of an image forming job so as to break up paper dust and toner clumps adhering to a blade edge. The broken paper dust and toner are discharged to the intermediate transfer belt. After that, the intermediate transfer belt is rotated in a forward direction, so that the paper dust and the toner are scraped off and collected by the cleaning blade.
Meanwhile, as a structure that transmits drive to a detachably attachable unit such as an intermediate transfer belt or a process cartridge, there are some related art coupling structures having a twisted polygonal shape. In such a coupling structure, engagement of a coupling is released by rotating the coupling in a reverse direction.
In order to rotate an image bearing body in the reverse direction with the coupling portions, the following method is used. Specifically, during the reverse rotation, forces in directions in which the engagement of the coupling portions is released act on the coupling portions due to the twisted polygonal shape. This moves away a rotating member. Accordingly, in order to prevent the rotating member from being moved away during the reverse rotation, the rotating member needs to be urged by an urging member that applies a greater urging force in a coupling engagement direction, which is opposite to the releasing direction, than the force acting due to the twisted polygonal shape. Furthermore, this urging force constantly, even when image formation is performed (that is, during forward rotation), acts on the components on the unit side such as the intermediate transfer belt or the process cartridge through the coupling portions. Thus, the position of the unit in the axial direction may become unstable. Accordingly, the unit side needs to be held by an urging force that is in an opposite direction to the direction of the urging force received from the rotating member and that is greater than the urging force received from the rotating member. Furthermore, even when the unit side is held by the greater urging force, the rotating member may be slightly misaligned in the engagement release direction of the coupling portions due to a force acting on the coupling portions during the reverse rotation depending on drive torque on the unit side. This may cause losses of drive transmission. Accordingly, when the reverse rotation is controlled as described above, the losses of the drive transmission is considered. This restricts a movement and time required for the control.